The fungal phytopathogen Leptosphaeria maculans, causing stem canker (blackleg) of rapeseed (Brassica napus), is mainly controlled worldwide by genetic resistance including major resistance genes (Rlm). This model is one of those for which the highest number of avirulence genes (AvrLm) has been cloned. In many systems, including L. maculans-B. napus interaction, intense use of resistance genes exerts strong selection pressure on the corresponding avirulent isolates, and the fungi may rapidly escape the resistance by various molecular events modifying the avirulence genes. In the literature, the study of polymorphism at avirulence loci is often focused on single genes under selection pressure. In this study, we investigate allelic polymorphism at eleven avirulence loci in a French population of 89 L. maculans isolates collected on a trap cultivar in four geographic locations in the 2017-2018 cropping season. The corresponding Rlm genes have been (i) used for a long time, (ii) recently used, or (iii) unused yet in agricultural practice. The sequence data generated indicate an extreme diversity of situations. For example, genes submitted to an ancient selection may have either been deleted in populations (AvrLm1) or replaced by a single-nucleotide mutated virulent version (AvrLm2, AvrLm5-9). Genes that have never been under selection may either be nearly invariant (AvrLm6, AvrLm10A, AvrLm10B), exhibit rare deletions (AvrLm11, AvrLm14), or display a high diversity of alleles and isoforms (AvrLmS-Lep2). These data suggest that the evolutionary trajectory of avirulence/virulence alleles is gene-dependent and selection pressure-independent in L. maculans.